Transmitter diversity technique for wireless communications

ABSTRACT

A simple block coding arrangement is created with symbols transmitted over a plurality of transmit channels, in connection with coding that comprises only of simple arithmetic operations, such as negation and conjugation. The diversity created by the transmitter utilizes space diversity and either time or frequency diversity. Space diversity is effected by redundantly transmitting over a plurality of antennas, time diversity is effected by redundantly transmitting at different times, and frequency diversity is effected by redundantly transmitting at different frequencies. Illustratively, using two transmit antennas and a single receive antenna, one of the disclosed embodiments provides the same diversity gain as the maximal-ratio receiver combining (MRRC) scheme with one transmit antenna and two receive antennas. The principles of this invention are applicable to arrangements with more than two antennas, and an illustrative embodiment is disclosed using the same space block code with two transmit and two receive antennas.

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/059,016, filed Sep. 16, 1997; of U.S. ProvisionalApplication No. 60/059,219, filed Sep. 18, 1997; and of U.S. ProvisionalApplication No. 60/063,780, filed Oct. 31, 1997.

BACKGROUND OF THE INVENTION

[0002] This invention relates to wireless communication and, moreparticularly, to techniques for effective wireless communication in thepresence of fading and other degradations.

[0003] The most effective technique for mitigating multipath fading in awireless radio channel is to cancel the effect of fading at thetransmitter by controlling the transmitter's power. That is, if thechannel conditions are known at the transmitter (on one side of thelink), then the transmitter can pre-distort the signal to overcome theeffect of the channel at the receiver (on the other side). However,there are two fundamental problems with this approach. The first problemis the transmitter's dynamic range. For the transmitter to overcome an xdB fade, it must increase its power by x dB which, in most cases, is notpractical because of radiation power limitations, and the size and costof amplifiers. The second problem is that the transmitter does not haveany knowledge of the channel as seen by the receiver (except for timedivision duplex systems, where the transmitter receives power from aknown other transmitter over the same channel). Therefore, if one wantsto control a transmitter based on channel characteristics, channelinformation has to be sent from the receiver to the transmitter, whichresults in throughput degradation and added complexity to both thetransmitter and the receiver.

[0004] Other effective techniques are time and frequency diversity.Using time interleaving together with coding can provide diversityimprovement. The same holds for frequency hopping and spread spectrum.However, time interleaving results in unnecessarily large delays whenthe channel is slowly varying. Equivalently, frequency diversitytechniques are ineffective when the coherence bandwidth of the channelis large (small delay spread).

[0005] It is well known that in most scattering environments antennadiversity is the most practical and effective technique for reducing theeffect of multipath fading. The classical approach to antenna diversityis to use multiple antennas at the receiver and perform combining (orselection) to improve the quality of the received signal.

[0006] The major problem with using the receiver diversity approach incurrent wireless communication systems, such as IS-136 and GSM, is thecost, size and power consumption constraints of the receivers. Forobvious reasons, small size, weight and cost are paramount. The additionof multiple antennas and RF chains (or selection and switching circuits)in receivers is presently not be feasible. As a result, diversitytechniques have often been applied only to improve the up-link (receiverto base) transmission quality with multiple antennas (and receivers) atthe base station. Since a base station often serves thousands ofreceivers, it is more economical to add equipment to base stationsrather than the receivers

[0007] Recently, some interesting approaches for transmitter diversityhave been suggested. A delay diversity scheme was proposed by A.Wittneben in “Base Station Modulation Diversity for Digital SIMULCAST,”Proceeding of the 1991 IEEE Vehicular Technology Conference (VTC 41 st),PP. 848-853, May 1991, and in “A New Bandwidth Efficient TransmitAntenna Modulation Diversity Scheme For Linear Digital Modulation,” inProceeding of the 1993 IEEE International Conference on Communications(IICC '93), PP. 1630-1634, May 1993. The proposal is for a base stationto transmit a sequence of symbols through one antenna, and the samesequence of symbols -but delayed - through another antenna.

[0008] U.S. Pat. No. 5,479,448, issued to Nambirajan Seshadri on Dec.26, 1995, discloses a similar arrangement where a sequence of codes istransmitted through two antennas. The sequence of codes is routedthrough a cycling switch that directs each code to the various antennas,in succession. Since copies of the same symbol are transmitted throughmultiple antennas at different times, both space and time diversity areachieved. A maximum likelihood sequence estimator (MLSE) or a minimummean squared error (MMSE) equalizer is then used to resolve multipathdistortion and provide diversity gain. See also N. Seshadri, J.H.Winters, “Two Signaling Schemes for Improving the Error Performance ofFDD Transmission Systems Using Transmitter Antenna Diversity,”Proceeding of the 1993 IEEE Vehicular Technology Conference (VTC 43rd),pp. 508-511, May 1993; and J. H. Winters, “The Diversity Gain ofTransmit Diversity in Wireless Systems with Rayleigh Fading,” Proceedingof the 1994 ICC/SUPERCOMM, New Orleans, Vol. 2, PP. 1121-1125, May 1994.

[0009] Still another interesting approach is disclosed by Tarokh,Seshadri, Calderbank and Naguib in U.S. application Ser. No. 08/847,635,filed Apr. 25, 1997 (based on a provisional application filed Nov. 7,1996), where symbols are encoded according to the antennas through whichthey are simultaneously transmitted, and are decoded using a maximumlikelihood decoder. More specifically, the process at the transmitterhandles the information in blocks of M1 bits, where M1 is a multiple ofM2, i.e., M1=k*M2. It converts each successive group of M2 bits intoinformation symbols (generating thereby k information symbols), encodeseach sequence of k information symbols into n channel codes (developingthereby a group of n channel codes for each sequence of k informationsymbols), and applies each code of a group of codes to a differentantenna.

SUMMARY

[0010] The problems of prior art systems are overcome, and an advance inthe art is realized with a simple block coding arrangement where symbolsare transmitted over a plurality of transmit channels and the codingcomprises only of simple arithmetic operations, such as negation andconjugation. The diversity created by the transmitter utilizes spacediversity and either time diversity or frequency diversity. Spacediversity is effected by redundantly transmitting over a plurality ofantennas; time diversity is effected by redundantly transmitting atdifferent times; and frequency diversity is effected by redundantlytransmitting at different frequencies. Illustratively, using twotransmit antennas and a single receive antenna, one of the disclosedembodiments provides the same diversity gain as the maximal-ratioreceiver combining (MRRC) scheme with one transmit antenna and tworeceive antennas. The novel approach does not require any bandwidthexpansion or feedback from the receiver to the transmitter, and has thesame decoding complexity as the MRRC. The diversity improvement is equalto applying maximal-ratio receiver combining (MRRC) at the receiver withthe same number of antennas. The principles of this invention areapplicable to arrangements with more than two antennas, and anillustrative embodiment is disclosed using the same space block codewith two transmit and two receive antennas. This scheme provides thesame diversity gain as four-branch MRRC.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a block diagram of a first embodiment in accordance withthe principles of this invention;

[0012]FIG. 2 presents a block diagram of a second embodiment, wherechannel estimates are not employed;

[0013]FIG. 3 shows a block diagram of a third embodiment, where channelestimates are derived from recovered signals; and

[0014]FIG. 4 illustrates an embodiment where two transmitter antennasand two receiver antennas are employed.

DETAIL DESCRIPTION

[0015] In accordance with the principles of this invention, effectivecommunication is achieved with encoding of symbols that comprises merelynegations and conjugations of symbols (which really is merely negationof the imaginary part) in combination with a transmitter createddiversity. Space diversity and either frequency diversity or timediversity are employed.

[0016]FIG. 1 presents a block diagram of an arrangement where the twocontrollable aspects of the transmitter that are used are space andtime. That is, the FIG. 1 arrangement includes multiple transmitterantennas (providing space diversity) and employs multiple timeintervals. Specifically, transmitter 10 illustratively comprisesantennas 11 and 12, and it handles incoming data in blocks n symbols,where n is the number of transmitter antennas, and in the illustrativeembodiment of FIG. 1, it equals 2, and each block takes n symbolintervals to transmit. Also illustratively, the FIG. 1 arrangementincludes a receiver 20 that comprises a single antenna 21.

[0017] At any given time, a signal sent by a transmitter antennaexperiences interference effects of the traversed channel, whichconsists of the transmit chain, the air-link, and the receive chain. Thechannel may be modeled by a complex multiplicative distortion factorcomposed of a magnitude response and a phase response. In the expositionthat follows therefore, the channel transfer function from transmitantenna 111 to receive antenna 21 is denoted by h₀ and from transmitantenna 12 to receive antenna 21 is denoted by h1, where:

h₀=α₀e^(jθ) ^(₀)

h₀=α₀e^(jθ) ^(₀)   (1)

[0018] Noise from interference and other sources is added at the tworeceived signals and, therefore, the resulting baseband signal receivedat any time and outputted by reception and amplification section 25 is

r(t)=α₀e^(jθ) ^(₀) s_(i)+α₁e^(jθ) ^(₁) s_(j)+n(t),  (2)

[0019] where s_(i) and s_(j) are the signals being sent by transmitantenna 11 and 12, respectively.

[0020] As indicated above, in the two-antenna embodiment of FIG. 1 eachblock comprises two symbols and it takes two symbol intervals totransmit those two symbols. More specifically, when symbols s_(i) ands_(j) need to be transmitted, at a first time interval the transmitterapplies signal se to antenna 111 and signal sj to antenna 12, and at thenext time interval the transmitter applies signal −s₁* to antenna 11 andsignal s₀* to antenna 12. This is clearly a very simple encoding processwhere only negations and conjugations are employed. As demonstratedbelow, it is as effective as it is simple. Corresponding to theabove-described transmissions, in the first time interval the receivedsignal is

r(t)=h₀s_(j)+h₁s_(j)+n(t),  (3)

[0021] and in the next time interval the received signal is

r(t+T)=−h₁s_(j)*+h₁s_(i)*+n(t+T).  (4)

[0022] Table 1 illustrates the transmission pattern over the twoantennas of the FIG. 1 arrangement for a sequence of signals {s₀,s₁, S₂,S₃, S₄, S₅, . . . }. TABLE 1 Time: t t + T t + 2T t + 3T t + 4T t + 5TAntenna 11 s₀ −s₁* s₂ −s₃* s₄ −s₅* . . . Antenna 12 s₁ s₀* s₃ s₂* s₅ s₄*. . .

[0023] The received signal is applied to channel estimator 22, whichprovides signals representing the channel characteristics or, rather,the best estimates thereof. Those signals are applied to combiner 23 andto maximum likelihood detector 24. The estimates developed by channelestimator 22 can be obtained by sending a known training signal thatchannel estimator 22 recovers, and based on the recovered signal thechannel estimates are computed. This is a well known approach.

[0024] Combiner 23 receives the signal in the first time interval,buffers it, receives the signal in the next time interval, and combinesthe two received signals to develop signals

{tilde over (s)}_(i)={tilde over (h)}₀*r(t)+{tilde over (h)}h₁r*(t+T)

{tilde over (s)}_(j)={tilde over (h)}₁*r(t)−{tilde over(h)}₀r*(t+T).  (5)

[0025] Substituting equation (1) into (5) yields

{tilde over (s)}i=({tilde over (α)}₀ ²+{tilde over (α)}₁ ²)S_(i)+{tildeover (h)}_(o)*n(t)+{tilde over (h)}₁n*(t+T)

{tilde over (s)}i=({tilde over (α)}₀ ²+{tilde over (α)}₁ ²)S_(i)+{tildeover (h)}_(o)*n(t)+{tilde over (h)}₁n*(t+T),  (6)

[0026] where {tilde over (α)}₀ ²={tilde over (h)}₀{tilde over (h)}₀* and{tilde over (α)}₁ ²={tilde over (h)}₁{tilde over (h)}₁* , demonstratingthat the signals of equation (6) are, indeed, estimates of thetransmitted signals (within a multiplicative factor). Accordingly, thesignals of equation (6) are sent to maximum likelihood detector 24.

[0027] In attempting to recover s_(i), two kind of signals areconsidered: the signals actually received at time t and t+T, and thesignals that should have been received if s_(i) were the signal that wassent. As demonstrated below, no assumption is made regarding. the valueof s_(j). That is, a decision is made that s_(i)=s_(x) for that value ofx for which

d²[r(t),(h₀s_(x)+h₁s_(j))]+d²[r(t+T),(−h₁s_(j)*+h₀s_(x)*)]

[0028] is less than

d²[r(t),(h₀s_(k)+h₁s_(j))]+d²[r(t+T),(−h₁s_(j)*+h₀s_(k)*)],  (7)

[0029] where d² (x,y) is the squared Euclidean distance between signalsx and y, i.e.,

d²(x, y)=|x−y|².

[0030] Recognizing that {tilde over (h)}₀=h₀+noise that is independentof the transmitted symbol, and that {tilde over (h)}₁=h₁+noise that isindependent of the transmitted symbol, equation (7) can be rewritten toyield

(α₀ ²+α₁ ²)|s_(x)|²−{tilde over (s)}_(i)s^(•) _(x)−{tilde over(s)}_(i)*S_(x)≦(α₀ ²+α₁ ²)|s_(k)|²−{tilde over (s)}_(i)s^(•) _(k)−{tildeover (s)}_(i)*s_(k)  (8)

[0031] where α₀ ²=h₀h₀* and α₁=h₁h₁*; or equivalently,

(α₀ ²+α₁ ²−1)|s_(x)|²+d²({tilde over (s)}_(i)s_(x))≦(α₀ ²+α₁ ²−1)|s_(k)|²+d²({tilde over (s)}_(i)s_(k)).  (9)

[0032] In Phase Shift Keying modulation, all symbols carry the sameenergy, which means that |s_(x)|²=|s_(k)|² and, therefore, the decisionrule of equation (9) may be simplified to

choose signal ŝ_(i)=s_(x)iff d²({tilde over (s)}_(i)s_(x))≦d²({tildeover (s)}_(i)s_(k)).  (10)

[0033] Thus, maximum likelihood detector 24 develops the signals S_(k)for all values of k, with the aid of {tilde over (h)}₀ and {tilde over(h)}₁ from estimator 22, develops the distances d²({tilde over(s)}_(i)s_(k)), identifies x for which equation (10) holds and concludesthat ŝ_(i)=s_(x). A similar process is applied for recovering ŝ_(j).

[0034] In the above-described embodiment each block of symbols isrecovered as a block with the aid of channel estimates {tilde over (h)}₀and {tilde over (h)}₁ . However, other approaches to recovering thetransmitted signals can also be employed. Indeed, an embodiment forrecovering the transmitted symbols exists where the channel transferfunctions need not be estimated at all, provided an initial pair oftransmitted signals is known to the receiver (for example, when theinitial pair of transmitted signals is prearranged). Such an embodimentis shown in FIG. 2, where maximum likelihood detector 27 is responsivesolely to combiner 26. (Elements in FIG. 3 that are referenced bynumbers that are the same as reference numbers in FIG. 1 are likeelements.) Combiner 26 of receiver 30 develops the signals

r₀=r(t)=h₀s₀+h₁s₁+n₀

r₁=r(t+T)=h₁s₀*−h₀s₁*+n₁

r₂=r(t+2T)=h₀s₂+h₁s₃+n₂

r₃=r(t+3T)=h₁s₂* −h₀s₃*+n₃,  (11)

[0035] then develops intermediate signals A and B

A=r_(O)r₃*−r₂ r₁*

B=r₂r₀*−r₁ r₃*,  (12)

[0036] and finally develops signals

{tilde over (s)}₂=As₁*+Bs₀

{tilde over (s)}₃=−As₀*+Bs₁,  (13)

[0037] where N₃ and N₄ are noise terms. It may be noted that signal r₂is actually r₂=h₀ŝ₂+h₁ŝ₃=h₀ŝ₂+h₁s₃+n₂, and similarly for signal r₃.Since the makeup of signals A and B makes them also equal to

A=(α₀ ²+α₁ ²)(s₂s₁−s₃s₀)+N₁

B=(α₀ ²+α₁ ²)(s₂s₀−s₃s₁)+N₂,  (14)

[0038] where N1 and N2 are noise terms, it follows that signals {tildeover (s)}₂ and {tilde over (s)}₃ are equal to

{tilde over (s)}₂=(α₀ ²+α₁ ²)(|S₀|²+|S₁|²)s₂+N₃

{tilde over (s)}₃=(α₀ ²+α₁ ²)(|S₀|²+|S₁|²)s₃+N₄ .  (15)

[0039] When the power of all signals is constant (and normalized to 1)equation (15) reduces to

{tilde over (s)}₂=(α₀ ²+α₁ ²)s₂+N₃

{tilde over (s)}₃=(α₀ ²+α₁ ²)s₃+N₄.  (16)

[0040] Hence, signals {tilde over (s)}₂ and {tilde over (s)}₃ are,indeed, estimates of the signals {tilde over (s)}₂ and {tilde over (s)}₃(within a multiplicative factor). Lines 28 and 29 demonstrate therecursive aspect of equation (13), where signal estimates {tilde over(s)}₂ and {tilde over (s)}₃ are evaluated with the aid of recoveredsignals {tilde over (s)}₀ and {tilde over (s)}₁ that are fed back fromthe output of the maximum likelihood detector.

[0041] Signals {tilde over (s)}₂ and {tilde over (s)}₃ are applied tomaximum likelihood detector 24 where recovery is effected with themetric expressed by equation (10) above. As shown in FIG. 2, oncesignals s₂ and s₃ are recovered, they are used together with receivedsignals r₂, r₃, r₄, and r₅ to recover signals s₄ and s₅, and the processrepeats.

[0042]FIG. 3 depicts an embodiment that does not require theconstellation of the transmitted signals to comprise symbols of equalpower. (Elements in FIG. 3 that are referenced by numbers that are thesame as reference numbers in FIG. 1 are like elements.) In FIG. 3,channel estimator 43 of receiver 40 is responsive to the output signalsof maximum likelihood detector 42. Having access to the recoveredsignals so and s₁, channel estimator 43 forms the estimates$\begin{matrix}\begin{matrix}{{\overset{\sim}{h}}_{0} = {\frac{{r_{0}s_{0}^{*}} - {r_{1}s_{1}}}{{s_{0}}^{2} + {s_{1}}^{2}} = {h_{0} + \frac{{s_{0}^{*}n_{0}} + {s_{1}n_{1}}}{{s_{0}}^{2} + {s_{1}}^{2}}}}} \\{{\overset{\sim}{h}}_{1} = {\frac{{r_{0}s_{1}^{*}} - {r_{1}s_{0}}}{{s_{0}}^{2} + {s_{1}}^{2}} = {h_{1} + \frac{{s_{1}^{*}n_{0}} + {s_{0}n_{1}}}{{s_{0}}^{2} + {s_{1}}^{2}}}}}\end{matrix} & (17)\end{matrix}$

[0043] and applies those estimates to combiner 23 and to detector 42.Detector 24 recovers signals s₂ and s₃ by employing the approach used bydetector 24 of FIG. 1, except that it does not employ the simplificationof equation (9). The recovered signals of detector 42 are fed back tochannel estimator 43, which updates the channel estimates in preparationfor the next cycle.

[0044] The FIGS. 1-3 embodiments illustrate the principles of thisinvention for arrangements having two transmit antennas and one receiveantenna. However, those principles are broad enough to encompass aplurality of transmit antennas and a plurality of receive antennas. Toillustrate, FIG. 4 presents an embodiment where two transmit antennasand two receive antennas are used; to wit, transmit antennas 31 and 32,and receive antennas 51 and 52. The signal received by antenna 51 isapplied to channel estimator 53 and to combiner 55, and the signalreceived by antenna 52 is applied to channel estimator 54 and tocombiner 55. Estimates of the channel transfer functions h₀ and h₁ areapplied by channel estimator 53 to combiner 55 and to maximum likelihooddetector 56. Similarly, estimates of the channel transfer functions h₂and h₃ are applied by channel estimator 54 to combiner 55 and to maximumlikelihood detector 56. Table 2 defines the channels between thetransmit antennas and the receive antennas, and table 3 defines thenotion for the received signals at the two receive antennas. TABLE 2Antenna 51 Antenna 52 Antenna 31 h₀ h₂ Antenna 32 h₁ h₃

[0045] TABLE 3 Antenna 51 Antenna 52 Time t r₀ r₂ Time t + T r₁ r₃

[0046] Based on the above, it can be shown that the received signals are

r₀=h₀s₀+h₁s₁+n₀

r₁=h₁s₀*−h₀s₁*+n₁

r₂=h₀s₂+h₁s₃+n₂

r₃=h₁s₂* −h₀s₃*+n₃(15)

[0047] where n₀,n₁,n₂, and n₃ are complex random variable representingreceiver thermal noise, interferences, etc.

[0048] In the FIG. 4 arrangement, combiner 55 develops the following twosignals that are sent to the maximum likelihood detector:

{tilde over (s)}₀=h₀*r₀+h₁r₁*+h₂*r₂+h₃r₃*

{tilde over (s)}₁=h₁*r₀+h₁r₁*+h₃*r₂−h₂r₃*.  (16)

[0049] Substituting the appropriate equations results in

{tilde over (s)}₀=(a₀ ²+a₁ ²+a₂ ²+a₃ ²)s₀+h₀*n₀+h₁n₁*+h₂*n₂+h₃n₃*

{tilde over (s)}₁=(a₀ ²+a₁ ²+a₂ ²+a₃ ²)s₁+h₁*n₀+h₀n₁*+h₃*n₂−h₂n₃*,  (17)

[0050] which demonstrates that the signal {tilde over (s)}₀ and {tildeover (s)}₁ are indeed estimates of the signals s₀ and s₁. Accordingly,signals {tilde over (s)}₀ and {tilde over (s)}₁ are sent to maximumlikelihood decoder 56, which uses the decision rule of equation (10) torecover the signals ŝ₀ and ŝ₁ .

[0051] As disclosed above, the principles of this invention rely on thetransmitter to force a diversity in the signals received by a receiver,and that diversity can be effected in a number of ways. The illustratedembodiments rely on space diversity—effected through a multiplicity oftransmitter antennas, and time diversity—effected through use of twotime intervals for transmitting the encoded symbols. It should berealized that two different transmission frequencies could be usedinstead of two time intervals. Such an embodiment would double thetransmission speed, but it would also increase the hardware in thereceiver, because two different frequencies need to be received andprocessed simultaneously.

[0052] The above illustrated embodiments are, obviously, merelyillustrative implementations of the principles of the invention, andvarious modifications and enhancements can be introduced by artisanswithout departing from the spirit and scope of this invention, which isembodied in the following claims. For example, all of the disclosedembodiments are illustrated for a space-time diversity choice, but asexplained above, one could choose the space-frequency pair. Such achoice would have a direct effect on the construction of the receivers.

We claim:
 1. An arrangement comprising: a coder responsive to incomingsymbols, forming a set of channel symbols that incorporate redundancy,where the coder employs replications and, at least for some of thechannel symbols, replications and negations; and an output stage thatapplies said channel symbols to at least one transmitter antenna to format least two distinct channels over a transmission medium.
 2. Thearrangement of claim 1 where said encoder replicates an incoming symbol,forms a negative of an incoming symbols, forms a complex conjugate of anincoming symbol, or forms a negative complex conjugate of an incomingsymbol.
 3. The arrangement of claim 1 where said coder carries out anencoding process that involves replications and negations.
 4. Thearrangement of claim 1 where said coder carries out an encoding processthat consists of replications and negations.
 5. The arrangement of claim1 where said at least two distinct channels direct information to asingle receiver antenna.
 6. The arrangement of claim 1 where each ofsaid at least two distinct channels transmits a channel symbol for eachincoming symbol encoded by said coder.
 7. The arrangement of claim 1where said coder encodes incoming symbols in blocks of n symbols.
 8. Thearrangement of claim 7 where, when n=2, the coder encodes an incomingblock of symbols s₀ and s₁ into a sequence of symbols s₀ and −s₁*, andinto a sequence of symbols s₁ and s₀ *, where s_(i) * is the complexconjugate of s_(i).
 9. The arrangement of claim 1 where said outputstage comprises a first antenna and a second antenna, and where inresponse to a sequence {s₀, s₁, s₂, s₃ , s₄, s₅ . . . } of incomingsymbols said coder develops a sequence {s₀*,−s₁*, s₂, −s₃ *, s₄, −s₅ *.. . } that is applied said first antenna by said output stage, and asequence {s₀*,s₃, s₂*, s₅ , s₄*, . . . } that is applied to said secondantenna by said output stage, where s_(i)* is the complex conjugate ofs_(i).
 10. The arrangement of claim 7 where said coder develops n·mchannel symbols for each block of n incoming symbols, where m is thenumber of said distinct channels.
 11. The arrangement of claim 10 wheresaid n·m channel symbols are distributed to said m distinct channels.12. The arrangement of claim 11 where said transmitter employs Ktransmitter antennas to effect K distinct channels, and where said n·mchannel symbols are distributed to said K antennas over L timeintervals, where K=m and L=n, or K=n and L=m.
 13. The arrangement ofclaim 11 where said transmitter employs K transmitter antennas to effectK distinct channels, and where said n·m channel symbols are distributedto said K antennas over L frequencies, where K=m and L=n, or K=n andL=m.
 14. The arrangement of claim 1 further comprising a receiver havinga single antenna that is adapted to receive and decode signalstransmitted by said output stage.
 15. The arrangement of claim 1 furthercomprising a receiver having two receive antennas that is adapted toreceive and decode signals transmitted by said output stage.
 16. Atransmitter comprising: first means, responsive to incoming symbols, forforming a set of channel symbols with redundancy in said set of channelsymbols, where the coder employs replications and, at least for some ofthe channel symbols, replications and negations to form said redundancy,and second means, for transmitting to a transmission medium channelsymbols formed by said first means over at least two antennas.
 17. Atransmitter comprising: first means for transmitting channel symbolsover two different and distinct transmitter channel types, therebyproviding transmitter-created diversity, where one of the channel typesis space diversity, and the other of the transmitter channel types istaken from a set including frequency diversity and time diversity; acoder for encoding incoming symbols in blocks of n symbols to form n mchannel symbols; and third means for distributing m groups of n channelsymbols each to said first means.
 18. The transmitter of claim 17 whereeach one of said groups is applied to a first of said distincttransmitter channels.
 19. The transmitter of claim 17 where one of saiddistinct transmitter channels is effected with a plurality oftransmitter antennas, providing space diversity, and another of saiddistinct transmitter channels is effected with a plurality of timeintervals.
 20. The transmitter of claim 19 where the number of saidtransmitter antennas is m and said m groups of channel symbols aredistributed to said m transmitter antennas.
 21. The transmitter of claim20 where n=2.
 22. A method for transmitting over a transmission mediuminformation corresponding to incoming symbols, comprising the steps of:encoding incoming symbols in block of n symbols, to form n·m channelsymbols, where m is a number of distinct space diverse channels overwhich said method transmits symbols over said transmission medium, wheresaid encoding involves replication of incoming symbols and, for at leastsome of said channel symbols, involve replication and negation; anddistributing said n·m channel symbols over said m channels so that eachincoming symbol has a corresponding channel symbol in each of said mchannels.
 23. The method of claim 22 where said encoding involvesforming a complex conjugate of incoming symbols.
 24. The method of claim22 where said encoding consists of replicating an incoming symbol,forming a complex conjugate of an incoming symbol, forming a negative ofan incoming symbols, or forming a negative complex conjugate of anincoming symbol.
 25. A method for transmitting information correspondingto incoming symbols, comprising the steps of: encoding incoming symbolsin block of n symbols, to form n·m channel symbols, where m is a numberof distinct space diverse channels over which said method transmitssymbols over said transmission medium; and distributing said n·m channelsymbols over said m channels so that each incoming symbol had acorresponding channel symbol in each of said m channels; where saidencoding involves replication of incoming symbols and, for at least someof said channel symbols, involves replication and negation operation.26. A receiver comprising: a combiner responsive to signals received byan antenna and to channel estimates developed for at least twoconcurrent space diverse paths over which said signals arrive at saidantenna, for developing sets of information symbol estimates, where saidcombiner develops said sets of information symbol estimates by combiningsaid signals received by said antenna with said channel estimates viaoperations that involve multiplications, negations, and conjugations;and a detector responsive to said sets of information symbol estimatesthat develops maximum likelihood decisions regarding information symbolsencoded into channel symbols and embedded in said signals received bysaid antenna.
 27. The receiver of claim 26 further comprising a channelestimator responsive to said signals received by said antenna fordeveloping said channel estimates.
 28. The receiver of claim 27 wheresaid channel estimator develops said channel estimates when said signalsreceived by said antenna contain a known sequence.
 29. The receiver ofclaim 27 where said signal received by said antenna at a given timeinterval corresponds to r(t)=h₀s_(i)+h₁s_(j)+n(t), and in a next timeinterval corresponds to r(t+T)=−h₀s_(j)*+h₁s_(i)*+n(t+T), where h₀ is atransfer function of a channel over which a symbol s_(i) is transmittedat said given time, h₀ is a transfer function of a channel over which asymbol s_(j), is transmitted at said given time interval, n(t) andn(t+T) are noise signals at said given time interval and said next timeinterval, respectively, and * appended to a signal designationrepresents the complex conjugate of the signal; and where said combinerforms a set of information symbol estimates comprising symbols {tildeover (s)}_(i) and {tilde over (s)}_(j) by forming signals {tilde over(s)}_(i)={tilde over (h)}₀*r(t)+{tilde over (h)}h₁r*(t+T)and sr=h *r(t)- h,r * (t+T) and {tilde over (s)}_(j)={tilde over (h)}₁*r(t)−{tildeover (h)}h₀r*(t+T) where {tilde over (h)}_(i) is the estimate of thechannel transfer function h_(i).
 30. The receiver of claim 29 where saiddetector settles on symbol ŝ_(i)=s_(x)iff d²({tilde over(s)}_(i)s_(x))≦d²({tilde over (s)}_(i)s_(k)), where d²({tilde over(s)}_(i)s_(x)) correspondsto (s_(i)−s_(x))(s_(i)*−s_(x)*).
 31. Thereceiver of claim 26 further comprising a channel estimator, responsiveto said sets of information symbols developed by said combiner, fordeveloping said channel estimates.
 32. The receiver of claim 26 furthercomprising a channel estimator, responsive to output signals of saiddetector, for developing said channel estimates.
 33. The receiver ofclaim 32 where said channel estimator develops channel estimates {tildeover (h)}₀ and {tilde over (h)}₁ by evaluating the expressions${\overset{\sim}{h}}_{0} = \frac{{r_{0}s_{0}^{*}} - {r_{1}s_{1}}}{{s_{0}}^{2} + {s_{1}}^{2}}$${\overset{\sim}{h}}_{1} = \frac{{r_{0}s_{1}^{*}} - {r_{1}s_{0}}}{{s_{0}}^{2} + {s_{1}}^{2}}$

where symbols s₀ and s₁ are output symbols of said detector, r₀ is asignal received at said antenna at a given time interval, r₁ is a signalreceived at said antenna at a next time interval, s_(i)* is the complexconjugate of s_(i), and |s_(i)|² is the magnitude, squared, of symbols_(i).
 34. A receiver comprising: a combiner responsive to signalsreceived by an antenna from space-diverse paths and to detectedinformation symbols, for developing sets of information symbolestimates, where said combiner develops said sets of information symbolestimates by combining said signals received by said antenna with saiddetected information symbols with operations that involvemultiplications, negations, and conjugations; and a detector responsiveto said sets of information symbol estimates that employs maximumlikelihood decisions regarding information symbols encoded into channelsymbols and embedded in said signals received by said antenna, todevelop thereby said detected information symbols.
 35. The receiver ofclaim 34 where said signal received by said antenna at a given timeinterval corresponds to r(t)=r(t)=r₀=h₀s₀+h₁s₁+n₀, and at subsequenttime intervals corresponds to r(t+T)=r₁=−h₀s₁+h₁s₀+n₁r(t+2T)=r₂=h₀s₂+h₁s₃+n₂and r(t+3T)=r₃=−h₀s₃+h₁s₂+n₃, where h₀ is atransfer function of a channel over which a symbol s₀ is transmitted atsaid given time interval, h₁ is a transfer function of a channel overwhich a symbol s₁ is transmitted at said given time interval, the nterms are noise signals, and * appended to a signal designationrepresents the complex conjugate of the signal; and where said combinerforms a set of information symbol estimates comprising symbols {tildeover (s)}₂ and {tilde over (s)}₃ by forming the signals {tilde over(s)}₃=As₁*+Bs₀ {tilde over (s)}₂=−As₀*+Bs₁, where A=r₀r₃*−r₂ r₁*. 36.The receiver of claim 26 where said combiner develops a set of ninformation symbols from n·m received channel symbols, where m is thenumber of concurrent paths for which said channel estimator developschannel estimates.
 37. A receiver comprising: a first channel estimatorresponsive to a first antenna, for developing two space- diverse channelestimates; a second channel estimator responsive to a second antenna,for developing two space-diverse channel estimates; a combinerresponsive to signals received by a first antenna and a second antennaand to channel estimates developed by said first and said second channelestimators, for developing sets of information symbol estimates, wheresaid combiner develops said sets of information symbol estimates bycombining said signals received by said antenna with said channelestimates obtained from said first and said second channel estimators,with operations that involve multiplications, negations, andconjugations; and a detector responsive to said sets of informationsymbol estimates that develops maximum likelihood decisions regardinginformation symbols encoded into channel symbols and embedded in saidsignals received by said first and second antennas.